1. Field of the Invention
The present invention relates to a sheet processing apparatus for performing processing on sheets and to an image forming apparatus equipped with this sheet processing apparatus. In particular, the present invention relates to a sheet processing apparatus which is endowed with a staple processing function for stapling an intermediate portion of a sheet bundle and which realizes a reduction in size through dimensional reduction in the height direction and the horizontal direction.
2. Related Background Art
Conventionally, there exists, for example, a sheet processing apparatus which staples sheets in the form of a bundle. This sheet processing apparatus is capable of a processing (so-called saddle stitching) in which sheets in the form of a bundle are stapled at the intermediate portion thereof and folded into a booklet. Such a sheet processing apparatus may be provided in the apparatus main body of an image forming apparatus as a component of the image forming apparatus (See JP 2000-153947 A).
FIG. 6 shows such an image forming apparatus. A conventional sheet processing apparatus 901 shown in FIG. 6 can perform saddle stitching as mentioned above, alignment processing for aligning an end portion of a sheet bundle (so-called sorting), side stitch binding for stapling an end portion of a sheet bundle (so-called staple sorting), etc.
That is, in the conventional sheet processing apparatus 901, sheets successively received from an apparatus main body 903 of an image forming apparatus 902 are stacked on a saddle stitching tray 910 formed as a substantially straight, steep slope, and are received by a stopper 911 to be formed into a bundle. Then, the sheet processing apparatus 901 performs width alignment on the sheets P by a width alignment device (not shown) before stapling the sheet bundle at two positions near the center thereof by an intermediate portion stapler unit 912. Thereafter, the sheet processing apparatus 901 moves the stopper 911, and causes the stapled portion of the sheet bundle to face the nip of a sheet folding roller pair 914 and a sheet thrusting plate 913. Then, the sheet processing apparatus 901 thrusts the stapled portion of the sheet bundle with the sheet thrusting plate 913, and feeds the sheet bundle to the nip of the sheet folding roller pair 914, folding the sheet bundle into two while nipping and conveying it by the sheet folding roller pair 914. Finally, the sheet processing apparatus 901 discharges the sheet bundle onto a sheet stacking portion 905 by a sheet discharging roller pair 915. In this way, the conventional sheet processing apparatus 901 shown in FIG. 6 is capable of performing saddle stitching to form a sheet bundle into a booklet by folding it into two.
Further, the conventional sheet processing apparatus 901 successively receives, on an intermediate tray 906, sheets P with images formed on one or both sides thereof in the apparatus main body 903 of the image forming apparatus 902, and, while doing so, performs width alignment on the sheets by a width alignment device 907 to form them into a bundle. Thereafter, the sheet processing apparatus 901 staples an end portion of the sheet bundle by an end stapler unit 908, and discharges the sheet bundle onto a sheet stacking portion 904 by a sheet discharging roller pair 909. In this way, the conventional sheet processing apparatus 901 shown in FIG. 6 is also capable of performing staple sorting.
FIG. 7 shows an image forming apparatus constructed so as to achieve a reduction in footprint. An image forming apparatus 921 has an image forming portion 922 in the lower portion thereof, an automatic original feeding apparatus 923 and an original reading device 924 in the upper portion thereof, and a sheet processing apparatus 925 in a sheet discharging space AR between the image forming portion 922 and the original reading device 924; thus, the image forming apparatus has a vertically elongated configuration to thereby achieve a reduction in footprint. As shown in FIGS. 7 through 9, the sheet processing apparatus 925 provided in the image forming apparatus 921 temporarily stacks sheets P with images thereon discharged from the image forming portion 922 on a processing tray 960 to form them into a bundle, and performs processing such as aligning and stapling on the sheet bundle before stacking the processed sheet bundle P on a discharge tray 961.
That is, in FIG. 8, the sheets P discharged from the image forming portion 922 (See FIG. 7) are further discharged onto the processing tray 960 from a discharging roller pair 941a, 941b. Then, the, sheets P are brought into contact with a trailing end stopper 943 through inclination of the processing tray 960 and rotation of a return belt 942, and the end portions extending perpendicular to the conveying direction are aligned. Further, alignment (width direction alignment) is effected on side portions extending along the sheet conveying direction by means of an aligning plate 944. In this way, the sheets successively discharged onto the processing tray 960 undergo alignment of the trailing ends and side portions to be formed into a bundle, and then an end portion of which is stapled by an end stapler 962.
The sheet bundle thus stapled is pressed against a swinging roller 948 mounted to a swinging arm 949 swingable in the direction indicated by the arrow A and in a direction opposite thereto, and is conveyed in the direction indicated by the arrow B through rotation of the swinging roller 948. Finally, the sheet bundle is discharged onto a discharge tray 961. When the sheet bundle is discharged onto the discharge tray 961, the swinging arm 949 returns to the position indicated by a chain double-dashed line in the drawing to make itself ready for next processing. When no stapling is effected in the above-described processing, the sheets, not stapled together, are discharged one by one onto the discharge tray 961 and stacked thereon.
In the sheet processing apparatus 901 shown in FIG. 6, capable of performing the above-described saddle stitching, the saddle stitching tray 910 accommodating sheets is linear, and the sheet thrusting plate 913, the sheet folding roller pair 914, and the stopper 911 are arranged linearly along the same, so that the length of the apparatus in the sheet conveying direction is rather large, which means the size of the apparatus tends to be rather large. Thus, it cannot be arranged in a space as shown in FIG. 7.
On the other hand, the sheet processing apparatus 925 shown in FIG. 7, which is arranged in the above-mentioned space, is not capable of performing saddle stitching.